Molding of pulp



Patented Nov. 30, 1937 UNITED STATES PATENT OFFICE MOLDING F PULPDelaware No Drawing. Application February 11, 1935, Serial No. 6,129

4 Claims. (Cl. 92-54) This invention relates to molding of pulp intofinished shapes and particularly to the molding of receptacles andcontainers, such as bottles and the like which are intended to hold.liquid 5 or semi-liquid materials, and to have smooth interior surfaces.

Although the molding of pulp containers, such as bottles, has long beenattempted, the results have not heretofore been altogether satisfactory.One reason for this has been the fact that the containers heretoforemade by molding pulp have had rough, uneven interior surfaces, which notonly were unsightly when inspected, but caused considerable loss ofcontents from clingage and failure to drain well when the containerswere emptied. Such loss has been considerable in amount when a largevolume of material such, for example, as lubricating oil, was dispensedin packages containing one quart or less.

The present invention consists primarily in a molding process which willproduce a smooth,-

even, surface or layer on the interior of the container. To this end,the process is conducted in stages, in which the pulp supply used toform the inner lining is in a much finer state of subdivision than thepulp deposited within the Walls of the container. Also the pulp ishydrated more highly and should be free working, although this propertymay be varied within wide limits depending on the use for which thearticle is intended.

The invention further relates to means for controlling both the rate andthe pressure at which the pulp particles are deposited in the outerportion of the body walls and in the interior surface or lining of thereceptacle. This is accomplished preferably by the use of pulp ofrelatively thick consistency when building up the body walls and by theuse of pulp in a highly diluted or attenuated state when finishing theinterior surface.

The invention further relates to the intro- "duction of a dispersingmedium in such a man- 45 ner that uneven deposits or lumps of pulpinitially deposited on the wall near the inner surface will be broken upand dispersed sufiiciently to permit the particles to be redeposited andthereby form a distinct inner layer having the so desiredcharacteristics with respect to fineness of pulp particles andsmoothness of finish.

The invention further consists in the new and novel features ofoperation and the new and original arrangements and combinations ofsteps in the process and also in a product having the generalcharacteristics, the new and useful applications, and the severalfeatures of utility hereinafter described and more particularly setforth in the claims.

In carrying out my improved process, the pulp is introduced in the formof a relatively thick suspension containing, for example, from 1% to 2%of pulp fibres. Water from the ordinary source of supply may be used,but preferably should be relatively free from suspended or dissolvedsubstances such as mud or calcium or magnesium compounds. Substantiallyall the pulp fibres have length of approximately 0.5 mm. to 3 mm.(millimeters), although this may vary within wide limits, depending uponthe type of article being molded.

The suspension is introduced into the mold, which may be perforated inthe usual way, through an inlet, which may or may not project a certaindistance into the mold. In the first stage, the pressure may vary fromone to ten pounds per square inch, comparatively low pressure beingdesirable, so that only normal conditions will obtain as the pulp flowsinto the mold and the walls gradually build up from the outer to theinner portion, until at least three fourths of the normal thickness ofthe walls has been deposited.

After the desired wall thickness has been obtained, to form the mainbody of the receptacle wall, the supply of pulp is cut off leaving theinterior of the mold filled with pulp suspension, with an appreciablequantity also of such suspension within the feed pipe from which it willdrain only slightly because, although the pressure is cut off, thethickness of the walls is sufficient to prevent rapid drainage of thewater. In this manner a layer of coarse pulp is laid against the moldwalls.

Promptly upon the closing of the first pulptank valve there isintroduced into the mold, under a pressure varying from 10 lbs. to lbs.per square inch, a /2% water suspension of fine pulp. This immediatelycauses quite rapid ebullition of the liquid Within the container and, atthe same time, it causes a washing or scouring action to take place overthe interior walls which,

at the pressure stated, is sufficient to loosen some of the pulpparticles and to disperse through the mixture any nodules, clots oraggregations of pulp that may have accumulated on the interior wallsduring the preceding stages of the process.

This action dilutes the first pulp suspension and, as the draining anddeposition take place,

the particles remaining in suspension and which were washed away fromthe surface tend to become finer and finer until eventually all of thepulp is deposited as a second layer and only clear Water remains.Generally speaking, the thinner pulp to form the second or inner layeris supplied to the mold for a period of approximately two to fiveseconds after it is first admitted so that loosening and redeposition ofpulp takes place to a considerable extent. Since the liquid tends toescape through the walls at the points where they are thinnest,innumerable currents are automatically set up to deposit pulp particlesat any point Where the liquid escapes and thus automatically thedepressions and valleys are filled up to or almost to the level of thethickest part of the interior wall, thus providing the container with asmooth interior surface.

Not only are the walls of the containers produced by my process of moreuniform thickness but the interior of the receptacle is smoother becauseof the selection that takes place automati cally with respect to pulpparticles. Ordinarily, the coarser particles will be first to depositand, unless they become imbedded and form projections or protuberancesWhere they are subjected to the washing action of the liquid currents,they tend to remain where placed by drainage. This causes the particlesremaining in suspension to become progressively finer and finer until atlast only the very fine particles are in suspension and are thendeposited on the Walls while the liquid drains away.

By means of this process, I am enabled to produce a smooth, even,finely-textured layer on the interior surface of a container withoutresorting to secondary treatments or to mechanical manipulation of anykind. Hence, the invention is well adapted to the manufacture of moldedpulp containers having restricted mouths or openings. The smooth wallsin the finished containers drain much more evenly and with less clingagethan walls having irregularities, such as projections and depressions,which tend to' withhold material even though it is not viscous incharacter. The steps of the operation follow immediately one after theother and very little more liquid is required than in the processesheretofore attempted.

By the process described, comprising the successive use of thicker andof thinner pulp suspensions, it has been possible to avoid the formationof rough interiors in molded pulp'containers and to cause the finerfibres to predominate there and to constitute a smooth felted innerlining which makes the container substantially free from clingage defectand consequent loss, and a new product in the molded pulp art.

While certain novel features of the invention have been disclosed andare pointed out in the annexed claims, it will be understood thatvarious omissions, substitutions and changes may be made by thoseskilled in the art without departing from the spirit of the invention.

What is claimed is 1. The herein described method of making molded paperpulp containers having substantially smooth interiors, which comprisessuccessive introduction into a foraminous mold, of a pulp suspensioncontaining 1%% to 2% of fibres, at a pressure of from one to 10 pounds,followed by a pulp suspension containing /4% to of fibres at a pressureof 10 lbs. to 30 lbs. per square inch, the duration of the flow of thickpulp suspension being shorter than that of the thin pulp suspension.

2. The method of making molded paper pulp containers havingsubstantially smooth interiors,

which comprises successive introduction through a nozzle into aforaminous mold, of a series of pulp suspensions, the first containing1%% to 2% of 0.5 mm. to 3 mm. pulp fibres, at a pressure not exceeding10 lbs. per square inch and continuing for a period not exceeding fiveseconds, the next pulp suspension containing about 0.5% of pulp, andintroduced under a higher pressure but not exceeding 30 lbs. per squareinch for a period not exceeding ten seconds, whereby to agitate thesecond pulp suspension and disperse lumpy aggregations of fibres andfinally to deposit said pulp in a layer having a smooth interiorsurface.

3. The method of making a molded pulp bottle having a restricted mouthin a foraminous mold having an interior shape like the desired exteriorshape of the bottle to be formed, which comprises introducing into saidmold a predetermined quantity of 1%% to 2% pulp suspension, under apressure not to exceed 10 lbs. per square inch, whereby to form a layerof substantial thickness upon the interior of said mold, thenintroducing into the container thereby formed a predetermined quantityof approximately 0.5% suspension of finer pulp under a pressureexceeding 10 lbs. per

square inch whereby to disperse any lumps of fibre previously depositedin said layer and to lay the fibres of said pulp in a second layerhaving a relatively smooth interior surface.

4. The method of molding a container from pulp which includesintroducing a liquid suspension of fibers into a foraminous mold under apressure not substantially in excess of 10 pounds per square inchtodeposit the fibers against the walls of the mold as a loosely moldedlayer, introducing a second suspension of finer fibers than said firstfibers, under a pressure substantially in excess of 20 pounds per squareinch to effect a compacting of the layer of fibers, and to causesufficient circulation currents in and agitation of the suspension toentrain deposits of fibers projecting from the layer and continuing theintroduction of said second suspension to smooth and level the layer anddeposit the finer fibers and entrained fibers on and in intermattingrelation with the fibers of said layer to form a smooth wall.

. ROY D. HEYMANN.

